Moulding by isostatic compression is a well-known technique in particular in the field of ceramics where it is used in combination with conventional methods of compression moulding and slip cast moulding.
The technique consists mainly in inserting powder in a suitable mould which is sealed then immersed in a liquid. The liquid is then subjected to high pressure by any suitable means. The resulting hydrostatic pressure is therefore transmitted to the powder by the walls of the mould and a moulded blank is thus formed which is then sintered to obtain the hard ceramic part.
However, a number of difficulties are encountered when using this technique.
In particular, in the case where tubes are to be manufactured, powder is inserted between the outer casing of the mould and a mandrel and the method described is used.
Now, on stripping the casting, it is observed that the part obtained extends slightly beyond the upper end of the mould where it can even break.
To overcome this drawback, a method has been proposed in which a cover is disposed at the upper end of the mould, between the outer casing and the mandrel and to provide the cover with an O ring designed to bear against said casing. Then, when the moulded tube extends beyond the upper end of the mould, said cover can slide between these two parts. However, the results of such a solution are not very satisfactory.
Preferred embodiments of the present invention provide a moulding apparatus for manufacturing tubular parts under hydrostatic pressure while avoiding breaking these parts and affording perfect sealing with respect to the surrounding liquid.